Understanding what everything is made of and how substances interact.
Why Chemistry Matters
Chemistry explains everyday experiences:
- Why oil and water don't mix
- How cooking transforms food
- Why some cleaners shouldn't be mixed
- How medications work in your body
- Why metals rust
- How batteries store energy
The Building Blocks
Atoms
Atoms are the smallest unit of an element that retains its properties.
| Part | Charge | Location | Mass |
|---|
| Proton | Positive (+) | Nucleus | 1 amu |
| Neutron | Neutral (0) | Nucleus | 1 amu |
| Electron | Negative (-) | Orbiting nucleus | Nearly 0 |
Key facts:
- Number of protons defines the element
- Atoms are mostly empty space
- Electrons determine chemical behavior
Elements
An element is a pure substance made of only one type of atom.
| Category | Examples | Properties |
|---|
| Metals | Iron, copper, gold | Conduct electricity, shiny, malleable |
| Nonmetals | Oxygen, carbon, nitrogen | Poor conductors, varied properties |
| Metalloids | Silicon, boron | Properties of both |
| Noble gases | Helium, neon, argon | Very unreactive |
Common Elements in Daily Life
| Element | Symbol | Where You Encounter It |
|---|
| Carbon | C | All living things, diamonds, graphite |
| Oxygen | O | Air we breathe, water |
| Hydrogen | H | Water, organic molecules |
| Nitrogen | N | Air (78%), fertilizers |
| Iron | Fe | Steel, blood hemoglobin |
| Calcium | Ca | Bones, teeth, milk |
| Sodium | Na | Table salt |
| Chlorine | Cl | Table salt, pool disinfectant |
| Aluminum | Al | Cans, foil, aircraft |
| Copper | Cu | Wires, pipes, coins |
Molecules and Compounds
Definitions
| Term | Meaning | Example |
|---|
| Molecule | Two or more atoms bonded together | O2 (oxygen gas) |
| Compound | Molecule with different elements | H2O (water) |
| Formula | Symbols showing composition | CO2 (1 carbon, 2 oxygen) |
Chemical Bonds
| Bond Type | How It Works | Strength | Example |
|---|
| Covalent | Atoms share electrons | Strong | Water (H2O) |
| Ionic | Electrons transferred, opposite charges attract | Strong | Salt (NaCl) |
| Metallic | Electrons shared across many atoms | Varies | Copper wire |
| Hydrogen | Weak attraction between molecules | Weak | Water sticking together |
Common Compounds
| Compound | Formula | Common Name/Use |
|---|
| H2O | Water | Life essential |
| NaCl | Sodium chloride | Table salt |
| CO2 | Carbon dioxide | Breathing out, carbonation |
| NaHCO3 | Sodium bicarbonate | Baking soda |
| CH4 | Methane | Natural gas |
| C6H12O6 | Glucose | Blood sugar |
| CaCO3 | Calcium carbonate | Limestone, antacids |
| H2O2 | Hydrogen peroxide | Disinfectant, bleaching |
States of Matter
The Four States
| State | Properties | Particle Behavior |
|---|
| Solid | Fixed shape and volume | Particles vibrate in place |
| Liquid | Fixed volume, takes container shape | Particles slide past each other |
| Gas | Expands to fill container | Particles move freely |
| Plasma | Ionized gas, conducts electricity | Electrons stripped from atoms |
Phase Changes
| Change | Direction | Example |
|---|
| Melting | Solid → Liquid | Ice to water |
| Freezing | Liquid → Solid | Water to ice |
| Evaporation | Liquid → Gas | Water drying up |
| Condensation | Gas → Liquid | Dew forming |
| Sublimation | Solid → Gas | Dry ice, frost disappearing |
| Deposition | Gas → Solid | Frost forming |
What Causes Phase Changes
| Factor | Effect |
|---|
| Adding heat | Particles move faster, may change to higher energy state |
| Removing heat | Particles slow down, may change to lower energy state |
| Changing pressure | Affects boiling point and phase transitions |
Chemical Reactions
What Happens in a Reaction
Reactants → Products
- Chemical bonds break and new ones form
- Atoms rearrange into new substances
- Mass is conserved (same atoms, different arrangement)
- Energy may be released or absorbed
Types of Reactions
| Type | What Happens | Example |
|---|
| Synthesis | A + B → AB | Hydrogen + oxygen → water |
| Decomposition | AB → A + B | Water → hydrogen + oxygen |
| Single replacement | A + BC → AC + B | Zinc + acid → zinc salt + hydrogen |
| Double replacement | AB + CD → AD + CB | Acid + base → salt + water |
| Combustion | Fuel + O2 → CO2 + H2O | Burning wood |
Signs a Reaction Has Occurred
| Sign | Example |
|---|
| Color change | Rust forming (orange-brown) |
| Gas produced | Baking soda + vinegar (bubbles) |
| Precipitate forms | Solid appears in liquid |
| Temperature change | Hand warmers (heat released) |
| Light produced | Glow sticks, fire |
Energy in Reactions
| Type | Energy | Example |
|---|
| Exothermic | Released (feels hot) | Combustion, hand warmers |
| Endothermic | Absorbed (feels cold) | Instant cold packs, photosynthesis |
Acids and Bases
The pH Scale
| pH | Classification | Examples |
|---|
| 0-2 | Strong acid | Battery acid, stomach acid |
| 3-4 | Weak acid | Vinegar, lemon juice |
| 5-6 | Slightly acidic | Coffee, rain |
| 7 | Neutral | Pure water |
| 8-9 | Slightly basic | Baking soda, seawater |
| 10-12 | Weak base | Ammonia, soapy water |
| 13-14 | Strong base | Bleach, drain cleaner |
Properties
| Property | Acids | Bases |
|---|
| Taste | Sour | Bitter |
| Feel | Sharp | Slippery |
| Reacts with metals | Yes (produces hydrogen) | Some |
| Indicator color | Turns litmus red | Turns litmus blue |
Neutralization
When an acid meets a base:
Acid + Base → Salt + Water
| Application | How It Works |
|---|
| Antacids | Base neutralizes stomach acid |
| Treating acid spills | Apply baking soda (base) |
| Soil treatment | Add lime to acidic soil |
Solutions and Mixtures
Types of Mixtures
| Type | Description | Example |
|---|
| Homogeneous | Uniform throughout | Salt water, air |
| Heterogeneous | Visibly different parts | Salad, sand in water |
| Solution | Solute dissolved in solvent | Sugar in water |
| Suspension | Particles that settle | Muddy water |
| Colloid | Particles that don't settle | Milk, fog |
Solution Terminology
| Term | Meaning | Example |
|---|
| Solvent | Substance that dissolves (larger amount) | Water in salt water |
| Solute | Substance dissolved (smaller amount) | Salt in salt water |
| Concentration | Amount of solute per solvent | Weak vs. strong coffee |
| Saturated | Maximum solute dissolved | No more sugar will dissolve |
| Supersaturated | More than normal dissolved | Creates crystals when disturbed |
Why Some Things Dissolve
"Like dissolves like"
| Solvent Type | Dissolves | Won't Dissolve |
|---|
| Polar (water) | Salt, sugar | Oil, grease |
| Nonpolar (oil) | Grease, wax | Salt, sugar |
This is why soap works: one end attaches to oil, the other to water.
Everyday Chemistry
In the Kitchen
| Activity | Chemistry |
|---|
| Baking | Heat causes chemical changes, leavening produces gas |
| Browning meat | Maillard reaction (amino acids + sugars) |
| Caramelization | Sugar breakdown at high heat |
| Marinating | Acids denature proteins, tenderizing meat |
| Emulsification | Combining oil and water (mayonnaise) |
Cleaning
| Product | How It Works |
|---|
| Soap | Molecules with water-loving and oil-loving ends |
| Bleach | Oxidizes (removes electrons from) stains |
| Baking soda | Mild base, neutralizes odors |
| Vinegar | Mild acid, dissolves mineral deposits |
Dangerous Combinations
| Never Mix | Produces | Danger |
|---|
| Bleach + Ammonia | Chloramine gas | Toxic fumes |
| Bleach + Vinegar | Chlorine gas | Toxic fumes |
| Different drain cleaners | Violent reaction | Explosion, burns |
| Hydrogen peroxide + Vinegar | Peracetic acid | Corrosive |
Chemistry in Your Body
Essential Reactions
| Process | Chemistry |
|---|
| Digestion | Enzymes break down food molecules |
| Respiration | Glucose + oxygen → energy + CO2 + water |
| Muscle movement | ATP releases energy |
| Blood pH | Buffers maintain pH 7.35-7.45 |
Medications
| How Drugs Work | Examples |
|---|
| Block receptors | Pain relievers, antihistamines |
| Mimic molecules | Insulin, hormone therapy |
| Kill organisms | Antibiotics |
| Change chemistry | Antacids, statins |
Practical Applications
Batteries
| Type | Chemistry |
|---|
| Alkaline | Zinc + manganese dioxide |
| Lithium-ion | Lithium moving between electrodes |
| Lead-acid (car) | Lead + sulfuric acid |
All batteries use chemical reactions to produce electricity.
Corrosion and Rust
| Process | What Happens |
|---|
| Rusting | Iron + oxygen + water → iron oxide |
| Prevention | Paint, galvanizing, stainless steel |
| Corrosion | Metal reacting with environment |
Plastics
| Fact | Details |
|---|
| What they are | Long chain molecules (polymers) |
| Made from | Petroleum products |
| Types | Thermoplastics (melt), thermosets (don't) |
| Recycling | Numbers indicate plastic type |
Key Takeaways
Everything is made of atoms - Just 118 elements combine to form all matter
Electrons determine behavior - Chemical properties come from electron arrangement
Bonds store energy - Breaking and forming bonds releases or absorbs energy
Mass is conserved - Atoms rearrange but aren't created or destroyed in reactions
Like dissolves like - Polar solvents dissolve polar substances, nonpolar dissolves nonpolar
pH matters - Acids and bases react together, and living things need specific pH
Don't mix household chemicals - Some combinations produce toxic gases
Cooking is chemistry - Heat and ingredients undergo real chemical changes
Your body runs on chemistry - Every biological process is a chemical reaction
Chemistry explains material properties - Why metals conduct, why plastics are flexible, why ice floats